Excessive risk taking underlies a range of pathological conditions, including drug addiction. Individual differences in risk taking may be an important determinant of both vulnerability to addiction and response to therapy, yet little is known about the neural basis underlying such differential vulnerability. Risk taking performance on the Balloon Analogue Risk Task (BART) paradigm showed robust and reliable individual difference, suggesting that BART performance may be representative of an individual's risk taking behavior phenotype. Using fMRI with the BART, our preliminary data has demonstrated that subjects'risk taking performance negatively correlated with the mesolimbic activation. This project will begin to evaluate the utility of both BOLD and ASL perfusion fMRI for characterizing the neural basis of inter-individual differences in risk taking in both healthy subjects and patients with cocaine addiction. While regional brain function will be assessed during the BART, this study will also explore the capability of characterizing individual risk taking phenotype based on measures of resting brain function that are independent of task context. The new knowledge gained from this study will have relevance for understanding and managing excessive risk taking in drug addiction and other impaired risk behaviors, and future studies may incorporate these measures as predictors of vulnerability or treatment response in substance abuse disorders. PUBLIC HEALTH RELEVANCE: Excessive risk taking and poor decision making is a hallmark behavioral phenotype of drug abusers and addicts. Although it is widely known that individuals differ in their vulnerability to drug abuse and other risk taking behaviors, little is known about the neurobiological basis underlying such individual differences. This project will use multimodal brain imaging techniques and the Balloon Analogue Risk Task (BART) paradigm to evaluate neural predictors of differential risk behavior phenotype in both healthy subjects and patients with cocaine addiction, and identify why some people are excessively risk-seeking that may be associated with vulnerability to drug abuse and addiction.